E309L-16 austenitic stainless steel electrodes for core components of nuclear island still rely on import,which severely restricts the development of nuclear power industry in China. The effect of the as-welded ferrite content on the elongation of the deposited metal after heat treatment at 608℃×40 h is studied. The microstructure of heat treated deposited metal with more than 12% as-welded ferrite is analyzed,and the effect of the heat input and heat preservation time on the tensile properties of the deposited metal is studied. The test results show that when the ferrite content is over 12%,the δ-ferrite decomposition is very uneven,which causes the elongation of the deposited metal after fracture to fluctuate greatly. The elongation may be less than 18%. When the ferrite content increases to 17.8%,most of the δ-ferrite decompose and the σ phase is precipitated,which is the cause of brittle fracture. The heat input and heat preservation time have little effect on the elongation of the deposited metal.